The present invention relates to an automotive vehicle brake system having a vacuum brake power booster which is interposed between brake pedal and master brake cylinder and which comprises at least two working chambers subdivided by a movable wall, one thereof communicating with the vacuum source, while the other one is adapted to be ventilated by means of a control valve actuatable by the brake pedal, with a view to generating a boosting force that is proportional to the brake pedal force, wherein wheel brake cylinders connect via brake lines to a primary and a secondary pressure chamber of the master brake cylinder, with sensors allocated to the wheels to be braked which sense the rotational behavior of the wheels in order to determine wheel-lock and whose output signals can be delivered to a central electronic control, the control signals of which serve to control electromagnetically actuatable pressure-fluid inlet and outlet valves inserted into the brake lines for slip control.
A brake system of this type is known, for instance, from German published patent application No. 36 27 000. The special feature of this known brake system operating with a hydraulic auxiliary-pressure supply system resides in that, in order to be able to quickly decrease the braking pressure generated by the master brake cylinder when a slip control action becomes necessary, the pistons of the master brake cylinder are provided with central regulating valves which, in the brake's release position, open pressure-fluid connections between a pressure-fluid supply reservoir and the pressure chambers of the master brake cylinder and close these pressure-fluid connections in the braking position, with the brake lines being in communication via supply lines containing non-return valves with the motively driven pumps of the auxiliary-pressure supply system, the intake ports of the pumps connecting via a suction line with the pressure-fluid supply reservoir.
What is to be regarded as less advantageous in the previously known brake system is the considerable structural effort which is required for generating and controlling the auxiliary hydraulic pressure, for resetting the master brake cylinder pistons as well as for safeguarding the braking function upon failure of individual brake circuits.
Therefore, an object of the present invention is to devise a brake system of the type initially referred to in such a fashion that there is achieved considerable reduction of the necessary manufacturing and assembling costs, while the system's reliability in operation is simultaneously increased. A further object is that the master cylinder pistons and, respectively, the brake pedal are to be reset completely after each slip control action.